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  <ul>
    <li><a href="#1-xml方式">1 xml方式</a></li>
    <li><a href="#2-注解方式">2 注解方式</a></li>
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            </div><div class="content" id="content"><p>spring源码系列文章，示例代码的中文注释，均是 copy 自 <a href="https://gitee.com/wlizhi/spring-framework" target="_blank" rel="noopener noreffer">https://gitee.com/wlizhi/spring-framework</a> 。</p>
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<hr>
<p>事务以xml配置方式使用时，xml是怎么解析，并将事务功能注册到容器中的？注解方式启动时，是怎么扫描注解将事务功能注册到容器中的？本文给出了详细的解析。</p>
<h2 id="1-xml方式">1 xml方式</h2>
<p>xml方式开启事务注解，是使用 <code>&lt;tx:annotation-driven/&gt;</code> 标签。根据 SPI 加载的规律，找到 <code>spring-tx</code> 包下的 <code>spring.handlers</code> 文件。</p>
<p>内容如下：</p>
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<pre tabindex="0" class="chroma"><code><span class="lnt">1
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<pre tabindex="0" class="chroma"><code class="language-fallback" data-lang="fallback"><span class="line"><span class="cl">http\://www.springframework.org/schema/tx=org.springframework.transaction.config.TxNamespaceHandler
</span></span></code></pre></td></tr></table>
</div>
</div><p>在 TxNamespaceHandler.init() 中，注册了事务相关标签的解析支持。</p>
<p>init() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">TxNamespaceHandler</span> <span class="kd">extends</span> <span class="n">NamespaceHandlerSupport</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">public</span> <span class="kt">void</span> <span class="nf">init</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// advice通知方法有关的，&lt;tx:advice /&gt; &lt;tx:attributes /&gt; &lt;tx:method /&gt; 标签支持在这里。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">registerBeanDefinitionParser</span><span class="o">(</span><span class="s">&#34;advice&#34;</span><span class="o">,</span> <span class="k">new</span> <span class="n">TxAdviceBeanDefinitionParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// &lt;tx:annotation-driven /&gt; 解析支持
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">registerBeanDefinitionParser</span><span class="o">(</span><span class="s">&#34;annotation-driven&#34;</span><span class="o">,</span> <span class="k">new</span> <span class="n">AnnotationDrivenBeanDefinitionParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 可以不看。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">registerBeanDefinitionParser</span><span class="o">(</span><span class="s">&#34;jta-transaction-manager&#34;</span><span class="o">,</span> <span class="k">new</span> <span class="n">JtaTransactionManagerBeanDefinitionParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>着重看 <code>&lt;tx:annotation-driven /&gt;</code> 标签的解析类，<code>&lt;tx:advice /&gt;</code> 解析支持原理类似。</p>
<p>直接来到方法 parse()：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">class</span> <span class="nc">AnnotationDrivenBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   <span class="kd">public</span> <span class="n">BeanDefinition</span> <span class="nf">parse</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// 当前方法注册了InfrastructureAdvisorAutoProxyCreator  Infrastructure--&gt;基础设施，优先级最低。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="c1">// 注意：区分@Aspect以及&lt;aop:aspectj-autoproxy/&gt;：两者注册的是AnnotationAwareAspectJAutoProxyCreator，最终按照优先级来确定使用哪个的。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		
</span></span><span class="line"><span class="cl">   		<span class="c1">// 注册事务事件监听器，@TransactionalEventListener注解的支持。可以不看。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="n">registerTransactionalEventListenerFactory</span><span class="o">(</span><span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="n">String</span> <span class="n">mode</span> <span class="o">=</span> <span class="n">element</span><span class="o">.</span><span class="na">getAttribute</span><span class="o">(</span><span class="s">&#34;mode&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// 根据mode的值，来确定注册哪种类型的事务支持。这个不常用，可以不看。着重看else里面的内容。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="k">if</span> <span class="o">(</span><span class="s">&#34;aspectj&#34;</span><span class="o">.</span><span class="na">equals</span><span class="o">(</span><span class="n">mode</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="c1">// mode=&#34;aspectj&#34;
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   			<span class="n">registerTransactionAspect</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="k">if</span> <span class="o">(</span><span class="n">ClassUtils</span><span class="o">.</span><span class="na">isPresent</span><span class="o">(</span><span class="s">&#34;javax.transaction.Transactional&#34;</span><span class="o">,</span> <span class="n">getClass</span><span class="o">().</span><span class="na">getClassLoader</span><span class="o">()))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   				<span class="n">registerJtaTransactionAspect</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   			<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="c1">// TODO 默认值是proxy，主要看这个。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   			<span class="c1">// mode=&#34;proxy&#34;
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   			<span class="n">AopAutoProxyConfigurer</span><span class="o">.</span><span class="na">configureAutoProxyCreator</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">parserContext</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">   	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>代码第一行注册了事务的事件监听，可以不看。</p>
<p>实际开发中，mode 属性基本不会配置，直接略过。默认值是 proxy。也就是说，会走到else代码块中。重点看 configureAutoProxyCreator()</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">private</span> <span class="kd">static</span> <span class="kd">class</span> <span class="nc">AopAutoProxyConfigurer</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">		<span class="kd">public</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">configureAutoProxyCreator</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">ParserContext</span> <span class="n">parserContext</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// TODO 注册Advisor
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">AopNamespaceUtils</span><span class="o">.</span><span class="na">registerAutoProxyCreatorIfNecessary</span><span class="o">(</span><span class="n">parserContext</span><span class="o">,</span> <span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">			<span class="c1">// 这里是一个常量，事务Advisor，等后面实例化时，如果匹配到方法，Advisor会封装到代理对象的执行链里面。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="n">String</span> <span class="n">txAdvisorBeanName</span> <span class="o">=</span> <span class="n">TransactionManagementConfigUtils</span><span class="o">.</span><span class="na">TRANSACTION_ADVISOR_BEAN_NAME</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(!</span><span class="n">parserContext</span><span class="o">.</span><span class="na">getRegistry</span><span class="o">().</span><span class="na">containsBeanDefinition</span><span class="o">(</span><span class="n">txAdvisorBeanName</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="n">Object</span> <span class="n">eleSource</span> <span class="o">=</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">extractSource</span><span class="o">(</span><span class="n">element</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// 创建AnnotationTransactionAttributeSource的BeanDefinition，这是一个策略接口的实现。用于获取事务注解的属性值。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Create the TransactionAttributeSource definition.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">RootBeanDefinition</span> <span class="n">sourceDef</span> <span class="o">=</span> <span class="k">new</span> <span class="n">RootBeanDefinition</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">						<span class="s">&#34;org.springframework.transaction.annotation.AnnotationTransactionAttributeSource&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">sourceDef</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">eleSource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">sourceDef</span><span class="o">.</span><span class="na">setRole</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">String</span> <span class="n">sourceName</span> <span class="o">=</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">().</span><span class="na">registerWithGeneratedName</span><span class="o">(</span><span class="n">sourceDef</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// 创建对应的MethodInterceptor，这是事务的方法拦截器，最终在生成代理的时候，会缓存到AdvisedSupport中，第一次调用执行生成执行链的时候，
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 如果匹配对应的方法，就会将方法名-MethodInterceptor的映射关系存储到执行链。同样是缓存到AdvisedSupport中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Create the TransactionInterceptor definition.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">RootBeanDefinition</span> <span class="n">interceptorDef</span> <span class="o">=</span> <span class="k">new</span> <span class="n">RootBeanDefinition</span><span class="o">(</span><span class="n">TransactionInterceptor</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">interceptorDef</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">eleSource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">interceptorDef</span><span class="o">.</span><span class="na">setRole</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="c1">// 注意，这里只注入了一个名字，PlatformTransactionManager需要我们手动注入到容器，在创建TransactionInterceptor时，会通过getBean()来获取
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">registerTransactionManager</span><span class="o">(</span><span class="n">element</span><span class="o">,</span> <span class="n">interceptorDef</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">interceptorDef</span><span class="o">.</span><span class="na">getPropertyValues</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;transactionAttributeSource&#34;</span><span class="o">,</span> <span class="k">new</span> <span class="n">RuntimeBeanReference</span><span class="o">(</span><span class="n">sourceName</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">				<span class="n">String</span> <span class="n">interceptorName</span> <span class="o">=</span> <span class="n">parserContext</span><span class="o">.</span><span class="na">getReaderContext</span><span class="o">().</span><span class="na">registerWithGeneratedName</span><span class="o">(</span><span class="n">interceptorDef</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">				<span class="c1">// 创建BeanFactoryTransactionAttributeSourceAdvisor的BeanDefinition，并注册到registry中。当bean在实例化，
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 查找容器中所有的增强方法时，会对所有的@Aspect封装成Advisor并实例化，以及直接注入进来的Advisor提前实例化，缓存到AdvisedSupport中。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// 从接口层面说，这里创建一个Advisor。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="c1">// Create the TransactionAttributeSourceAdvisor definition.
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>				<span class="n">RootBeanDefinition</span> <span class="n">advisorDef</span> <span class="o">=</span> <span class="k">new</span> <span class="n">RootBeanDefinition</span><span class="o">(</span><span class="n">BeanFactoryTransactionAttributeSourceAdvisor</span><span class="o">.</span><span class="na">class</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">advisorDef</span><span class="o">.</span><span class="na">setSource</span><span class="o">(</span><span class="n">eleSource</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">advisorDef</span><span class="o">.</span><span class="na">setRole</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="n">advisorDef</span><span class="o">.</span><span class="na">getPropertyValues</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;transactionAttributeSource&#34;</span><span class="o">,</span> <span class="k">new</span> <span class="n">RuntimeBeanReference</span><span class="o">(</span><span class="n">sourceName</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">				<span class="n">advisorDef</span><span class="o">.</span><span class="na">getPropertyValues</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;adviceBeanName&#34;</span><span class="o">,</span> <span class="n">interceptorName</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">				<span class="k">if</span> <span class="o">(</span><span class="n">element</span><span class="o">.</span><span class="na">hasAttribute</span><span class="o">(</span><span class="s">&#34;order&#34;</span><span class="o">))</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">					<span class="n">advisorDef</span><span class="o">.</span><span class="na">getPropertyValues</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;order&#34;</span><span class="o">,</span> <span class="n">element</span><span class="o">.</span><span class="na">getAttribute</span><span class="o">(</span><span class="s">&#34;order&#34;</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">				<span class="o">}</span>
</span></span><span class="line"><span class="cl">				<span class="n">parserContext</span><span class="o">.</span><span class="na">getRegistry</span><span class="o">().</span><span class="na">registerBeanDefinition</span><span class="o">(</span><span class="n">txAdvisorBeanName</span><span class="o">,</span> <span class="n">advisorDef</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">                <span class="c1">// 剩余源码省略 ...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从上面源码中可以看到，分别注册了 <code>TransactionAttributeSource</code>、<code>MethodInterceptor（也是Advice）</code>、<code>Advisor</code>的BeanDefinition对象，其中后面两个是利用AOP模块功能生成动态代理的关键接口。
而 <code>TransactionAttributeSource</code> 是对事务属性解析的支持。</p>
<p>这些动作是在解析标签的时候做的，然后经历 BeanFactoryPostProcessor 的后置方法执行、以及 BeanPostProcessor 的注册之后，最终执行到将BeanDefinition中封装的类信息实例化时，会创建上面源码中注册的三个实例。
而在创建实例、依赖注入、执行完bean的初始化方法后，最终会执行到 BeanPostProcessor.postProcessAfterInitialization()，而 AbstractAutoProxyCreator（也是一个BeanPostProcessor） 的子类（激活了自动代理功能），
会搜集beanDefinitions中所有的Advisor类型的beanDefinition，对其实例化，封装到AdvisedSupport中，如果对象需要被代理，则会将AdvisedSupport封装到代理对象中。最终在调用代理对象方法的时候，会生成代理方法的执行链。</p>
<p>由于 TransactionInterceptor 实现了 InitializingBean。在bean实例化完成后，会调用 afterPropertiesSet()，来看一下这个方法：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">abstract</span> <span class="kd">class</span> <span class="nc">TransactionAspectSupport</span> <span class="kd">implements</span> <span class="n">BeanFactoryAware</span><span class="o">,</span> <span class="n">InitializingBean</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   <span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">   	<span class="kd">public</span> <span class="kt">void</span> <span class="nf">afterPropertiesSet</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   		<span class="c1">// 开启事务支持，那么PlatformTransactionManager和TransactionAttributeSource这两个实例是必须有的，否则启动就会抛出异常。
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>   		<span class="k">if</span> <span class="o">(</span><span class="n">getTransactionManager</span><span class="o">()</span> <span class="o">==</span> <span class="kc">null</span> <span class="o">&amp;&amp;</span> <span class="k">this</span><span class="o">.</span><span class="na">beanFactory</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="k">throw</span> <span class="k">new</span> <span class="n">IllegalStateException</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">   					<span class="s">&#34;Set the &#39;transactionManager&#39; property or make sure to run within a BeanFactory &#34;</span> <span class="o">+</span>
</span></span><span class="line"><span class="cl">   					<span class="s">&#34;containing a PlatformTransactionManager bean!&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   		<span class="k">if</span> <span class="o">(</span><span class="n">getTransactionAttributeSource</span><span class="o">()</span> <span class="o">==</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">   			<span class="k">throw</span> <span class="k">new</span> <span class="n">IllegalStateException</span><span class="o">(</span>
</span></span><span class="line"><span class="cl">   					<span class="s">&#34;Either &#39;transactionAttributeSource&#39; or &#39;transactionAttributes&#39; is required: &#34;</span> <span class="o">+</span>
</span></span><span class="line"><span class="cl">   					<span class="s">&#34;If there are no transactional methods, then don&#39;t use a transaction aspect.&#34;</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">   		<span class="o">}</span>
</span></span><span class="line"><span class="cl">   	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从源码中可以看到，如果开启了事务功能，PlatformTransactionManager、TransactionAttributeSource是必不可少的，否则容器启动就会抛出异常。</p>
<p>而在上面源码中，TransactionAttributeSource已经设置了，而PlatformTransactionManager只注册了一个beanName，
这需要我们指定注入到ioc容器中。例如传统spring项目中使用的 DataSourceTransactionManager 就是使用bean标签注入的。</p>
<blockquote>
<p>题外话：之所以 springboot 中我们不用创建 PlatformTransactionManager，是因为 auto-configuration 模块，使用 SPI 的方式，导入了 DataSourceTransactionManagerAutoConfiguration。</p>
</blockquote>
<p>从下面代码就可以看出，TransactionInterceptor中仅仅注册了一个PlatformTransactionManager的beanName：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">class</span> <span class="nc">AnnotationDrivenBeanDefinitionParser</span> <span class="kd">implements</span> <span class="n">BeanDefinitionParser</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">    <span class="kd">private</span> <span class="kd">static</span> <span class="kt">void</span> <span class="nf">registerTransactionManager</span><span class="o">(</span><span class="n">Element</span> <span class="n">element</span><span class="o">,</span> <span class="n">BeanDefinition</span> <span class="n">def</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="n">def</span><span class="o">.</span><span class="na">getPropertyValues</span><span class="o">().</span><span class="na">add</span><span class="o">(</span><span class="s">&#34;transactionManagerBeanName&#34;</span><span class="o">,</span>
</span></span><span class="line"><span class="cl">				<span class="n">TxNamespaceHandler</span><span class="o">.</span><span class="na">getTransactionManagerName</span><span class="o">(</span><span class="n">element</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><h2 id="2-注解方式">2 注解方式</h2>
<p>在使用注解方式激活@Transaction支持时，使用的是@EnableTransactionManagement，在这个注解声明中可以看到，使用了@Import导入TransactionManagementConfigurationSelector。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="nd">@Target</span><span class="o">(</span><span class="n">ElementType</span><span class="o">.</span><span class="na">TYPE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Retention</span><span class="o">(</span><span class="n">RetentionPolicy</span><span class="o">.</span><span class="na">RUNTIME</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="nd">@Documented</span>
</span></span><span class="line"><span class="cl"><span class="c1">// TODO 重点：事务注册入口类
</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="nd">@Import</span><span class="o">(</span><span class="n">TransactionManagementConfigurationSelector</span><span class="o">.</span><span class="na">class</span><span class="o">)</span>
</span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="nd">@interface</span> <span class="n">EnableTransactionManagement</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl"><span class="c1">// 省略...
</span></span></span><span class="line"><span class="cl"><span class="c1"></span><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>在spring容器启动时，就会加载TransactionManagementConfigurationSelector，调用 selectImports()，在这个方法中，就添加了两个类的支持。</p>
<p>selectImports() 源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">TransactionManagementConfigurationSelector</span> <span class="kd">extends</span> <span class="n">AdviceModeImportSelector</span><span class="o">&lt;</span><span class="n">EnableTransactionManagement</span><span class="o">&gt;</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Override</span>
</span></span><span class="line"><span class="cl">	<span class="kd">protected</span> <span class="n">String</span><span class="o">[]</span> <span class="nf">selectImports</span><span class="o">(</span><span class="n">AdviceMode</span> <span class="n">adviceMode</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">switch</span> <span class="o">(</span><span class="n">adviceMode</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">case</span> <span class="n">PROXY</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="k">new</span> <span class="n">String</span><span class="o">[]</span> <span class="o">{</span><span class="n">AutoProxyRegistrar</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getName</span><span class="o">(),</span>
</span></span><span class="line"><span class="cl">						<span class="n">ProxyTransactionManagementConfiguration</span><span class="o">.</span><span class="na">class</span><span class="o">.</span><span class="na">getName</span><span class="o">()};</span>
</span></span><span class="line"><span class="cl">			<span class="k">case</span> <span class="n">ASPECTJ</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="k">new</span> <span class="n">String</span><span class="o">[]</span> <span class="o">{</span><span class="n">determineTransactionAspectClass</span><span class="o">()};</span>
</span></span><span class="line"><span class="cl">			<span class="k">default</span><span class="o">:</span>
</span></span><span class="line"><span class="cl">				<span class="k">return</span> <span class="kc">null</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>从上面源码中可以看到，共添加了两个类，主要看 ProxyTransactionManagementConfiguration 这个类。</p>
<p>在这个类中，定义了三个方法，使用@Bean，向容器中注入了BeanFactoryTransactionAttributeSourceAdvisor、TransactionInterceptor、AnnotationTransactionAttributeSource。这三个分别是Advisor、Advice（MethodInterceptor）、TransactionAttributeSource的实现类。</p>
<p>源码如下：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="nd">@Configuration</span>
</span></span><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">ProxyTransactionManagementConfiguration</span> <span class="kd">extends</span> <span class="n">AbstractTransactionManagementConfiguration</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Bean</span><span class="o">(</span><span class="n">name</span> <span class="o">=</span> <span class="n">TransactionManagementConfigUtils</span><span class="o">.</span><span class="na">TRANSACTION_ADVISOR_BEAN_NAME</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Role</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">BeanFactoryTransactionAttributeSourceAdvisor</span> <span class="nf">transactionAdvisor</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 事务切面类
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">BeanFactoryTransactionAttributeSourceAdvisor</span> <span class="n">advisor</span> <span class="o">=</span> <span class="k">new</span> <span class="n">BeanFactoryTransactionAttributeSourceAdvisor</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">advisor</span><span class="o">.</span><span class="na">setTransactionAttributeSource</span><span class="o">(</span><span class="n">transactionAttributeSource</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="n">advisor</span><span class="o">.</span><span class="na">setAdvice</span><span class="o">(</span><span class="n">transactionInterceptor</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">enableTx</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">advisor</span><span class="o">.</span><span class="na">setOrder</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">enableTx</span><span class="o">.&lt;</span><span class="n">Integer</span><span class="o">&gt;</span><span class="n">getNumber</span><span class="o">(</span><span class="s">&#34;order&#34;</span><span class="o">));</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">advisor</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Bean</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Role</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">TransactionAttributeSource</span> <span class="nf">transactionAttributeSource</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// TODO 事务属性解析类
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">return</span> <span class="k">new</span> <span class="n">AnnotationTransactionAttributeSource</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="nd">@Bean</span>
</span></span><span class="line"><span class="cl">	<span class="nd">@Role</span><span class="o">(</span><span class="n">BeanDefinition</span><span class="o">.</span><span class="na">ROLE_INFRASTRUCTURE</span><span class="o">)</span>
</span></span><span class="line"><span class="cl">	<span class="kd">public</span> <span class="n">TransactionInterceptor</span> <span class="nf">transactionInterceptor</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 事务拦截器
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="n">TransactionInterceptor</span> <span class="n">interceptor</span> <span class="o">=</span> <span class="k">new</span> <span class="n">TransactionInterceptor</span><span class="o">();</span>
</span></span><span class="line"><span class="cl">		<span class="n">interceptor</span><span class="o">.</span><span class="na">setTransactionAttributeSource</span><span class="o">(</span><span class="n">transactionAttributeSource</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">txManager</span> <span class="o">!=</span> <span class="kc">null</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="n">interceptor</span><span class="o">.</span><span class="na">setTransactionManager</span><span class="o">(</span><span class="k">this</span><span class="o">.</span><span class="na">txManager</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">return</span> <span class="n">interceptor</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>xml方式注入中，也是像容器中注入了这几个类。同样创建的流程也都是一样的。
<span id="AnnotationTransactionAttributeSource"></span></p>
<p>接着看一下 AnnotationTransactionAttributeSource，在创建实例的时候，封装了对@Transactional的支持。</p>
<p>来到构造方法源码：</p>
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<pre tabindex="0" class="chroma"><code class="language-java" data-lang="java"><span class="line"><span class="cl"><span class="kd">public</span> <span class="kd">class</span> <span class="nc">AnnotationTransactionAttributeSource</span> <span class="kd">extends</span> <span class="n">AbstractFallbackTransactionAttributeSource</span>
</span></span><span class="line"><span class="cl">		<span class="kd">implements</span> <span class="n">Serializable</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">	<span class="c1">// 步骤一
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="kd">public</span> <span class="nf">AnnotationTransactionAttributeSource</span><span class="o">()</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="k">this</span><span class="o">(</span><span class="kc">true</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl">
</span></span><span class="line"><span class="cl">	<span class="c1">// 步骤二
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>	<span class="kd">public</span> <span class="nf">AnnotationTransactionAttributeSource</span><span class="o">(</span><span class="kt">boolean</span> <span class="n">publicMethodsOnly</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">		<span class="c1">// 这里注入了注解解析类。 SpringTransactionAnnotationParser，解析时就用到的这个类中的方法
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>		<span class="k">this</span><span class="o">.</span><span class="na">publicMethodsOnly</span> <span class="o">=</span> <span class="n">publicMethodsOnly</span><span class="o">;</span>
</span></span><span class="line"><span class="cl">		<span class="k">if</span> <span class="o">(</span><span class="n">jta12Present</span> <span class="o">||</span> <span class="n">ejb3Present</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">this</span><span class="o">.</span><span class="na">annotationParsers</span> <span class="o">=</span> <span class="k">new</span> <span class="n">LinkedHashSet</span><span class="o">&lt;&gt;(</span><span class="n">4</span><span class="o">);</span>
</span></span><span class="line"><span class="cl">            <span class="c1">// TODO 重点看这里
</span></span></span><span class="line"><span class="cl"><span class="c1"></span>			<span class="k">this</span><span class="o">.</span><span class="na">annotationParsers</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">SpringTransactionAnnotationParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">jta12Present</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">this</span><span class="o">.</span><span class="na">annotationParsers</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">JtaTransactionAnnotationParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">			<span class="k">if</span> <span class="o">(</span><span class="n">ejb3Present</span><span class="o">)</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">				<span class="k">this</span><span class="o">.</span><span class="na">annotationParsers</span><span class="o">.</span><span class="na">add</span><span class="o">(</span><span class="k">new</span> <span class="n">Ejb3TransactionAnnotationParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">			<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">		<span class="k">else</span> <span class="o">{</span>
</span></span><span class="line"><span class="cl">			<span class="k">this</span><span class="o">.</span><span class="na">annotationParsers</span> <span class="o">=</span> <span class="n">Collections</span><span class="o">.</span><span class="na">singleton</span><span class="o">(</span><span class="k">new</span> <span class="n">SpringTransactionAnnotationParser</span><span class="o">());</span>
</span></span><span class="line"><span class="cl">		<span class="o">}</span>
</span></span><span class="line"><span class="cl">	<span class="o">}</span>
</span></span><span class="line"><span class="cl"><span class="o">}</span>
</span></span></code></pre></td></tr></table>
</div>
</div><p>在构造方法中，封装了SpringTransactionAnnotationParser对象。</p>
<p>这个类是对@Transactional注解的支持，在bean实例化完成之后，调用代理方法执行时，首先会生成执行链，然后按照索引顺序递归调用执行链。
在调用到事务的节点时，会获取事务属性对象，通过事务属性来被代理方法中@Transactional注解中配置的属性值。以此来判断是否开启事务、以及设置事务隔离级别、传播行为等属性值。</p>
<p>SpringTransactionAnnotationParser中具体有哪些方法，执行了哪些行为，在声明式事务执行流程源码分析中会详细列出。</p></div>

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